V3.57 active flyback 95lb Low impedance injector issue

[jracer99]

Hi guys,
I have a Preassembled from DIY, MS2 v3.57 running 2.886 code on a turbo 2.4L GM engine. I have had great luck with the system, tuned great and making awesome power. I had 42LB high impendence injectors. I just swapped to 95LB low impedance injectors using the flyback circuit. I did the procedures in the tuning section for tuning the PWM of the injectors. PWM Time Threshold = 1.0 millisecond and PWM Current Limit (%) = 30%
Then I did the steps of lowering the current limit. However I lowered this value by one point at a time all the way to a value of 1 and the idle quality never change. It idled great the whole time. I burned the value each time to the MS2. I then put it back to 30 to be safe. Is this normal? I don’t want to burn anything up. injectors are from DIY too.

Then the next step is to adjust the PWM Time Threshold until idle quality changed. I got this value to .8 then the idle quality got worse. I increased it back up 3% like the directions said and the idle is smooth. But still worried about the above issue.

I let the car idle smooth for quite a while to adjust fuel pressure and VE values to get a good Air Fuel ratio when I noticed a blip in the idle quality, intermittently and spaced out just like a hiccup. I was able to capture it in a data log. What the data log indicates is that the injector pulse cut out freakishly. Any Ideas? I don’t want to drive it with this issue and its getting nice out.

[Matt Cramer]

30% should be fine. Just make sure the items on the heat sink aren't running hot.

[jracer99]

Is it normal for that setting not to affect idle quality while reducing it down to 1 though?

Did you get a chance to look at the data log I attached. I have an inconsistent hiccup in the idle. Do you think that my idle pulse width being about 1.2ms and my injector open time is 1ms could affect this? these are very large injectors for this engine and had to tune them way down to idle at 13.5 afr. I could increase idle speed and see if it goes away. or switch to alternating injector fire instead of simultaneously. But the fact that there is a hiccup and that the pwm current limit adjustment did nothing worries me. I will check the heat sink

Maybe I just need to set idle speed higher to alow for more injector puls width at idle.

[Matt Cramer]

When your pulse width is very close to the injector opening time, the usual method of tuning the PWM criteria doesn't work too well. A value so small the injectors start closing can still keep them open long enough that it doesn't change the idle quality.

[jracer99]

Thanks Matt, That is exactly what I thought.
Now what about this. Why would injectors twice the size (1000cc) of the ones I replaced (440cc) require much Higher VE values in the map.
I tried to drive and tune last night and the car was way leaner than with the lower flow 440cc injectors
It also looks like my data quality in my logs is worse too. The traces are not as smooth.

The heat sink does not get hot at 30% curent limit.

What is the best way to get your fuel right when you have an awesome map on lower flow injectors and you up to higher flow injectors? I re-did the required fuel adjustment. do I need to generate a new map and start all over?

Im going to play around maybe I got a corupt file or something.

[Matt Cramer]

Could be the opening time wasn't quite right - when going to larger injectors getting the opening timing nailed is critical.

[jracer99]

Yeah I got the injector opening time nailed. I figgured out why the maps were so off and hopefully this can be a lesson learned and save some one some trouble.

These injectors are very large for my apication at idle and it was difficult to tune because the idle injector pulse width is only 1.4ms. I re-adjusted the required fuel function for the maps I had for the 42lb injectors to allow for the 95 lb injectors. My idle air fuel ratio was still very rich 11.8. So I lowered my fuel rail pressure down several psi. Then my VE maps needed a lot larger values than normal. Then I realized that messing with fuel pressure actually lowered the effective flow rate of the injectors thus the lean conditions while driving and much higher VE values. I calculated the new injector flow rate with the lower fuel pressure, set this new value in the required fuel function, and reflashed my original maps. Tuning was then a breeze and much more accurate.

I still have one question and concern about the current limit, because I am still concerned that it is not optimized at 30%. Now that I have a good map, do you think I could get to a safe driving condition, with a little larger injector pulse width, turn of the closed loop EGO feed back and start lowering the current limit value until the running quality changes or air fuel ratio changes? Tune it that way instead at idle?